libstdc++: Ensure c++NN effective-target present in more tests

libstdc++: Ensure c++NN effective-target present in more tests

Add effective-target keywords to tests that would fail for certain
standard modes without the -std=gnu++NN option.

libstdc++-v3/ChangeLog:

	* testsuite/18_support/set_terminate.cc: Require C++11 or
	higher.
	* testsuite/28_regex/simple_c++11.cc: Likewise.
	* testsuite/tr1/headers/c++200x/complex.cc: Likewise.
	* testsuite/24_iterators/headers/iterator/synopsis.cc:
	Require C++14 or lower.